This invention relates generally to devices for combining the outputs of multiple lasers, and more particularly, to laser combiners intended to provide a highly coherent composite laser beam. There is a need in a variety of fiber-optic and communication systems for a high-power pulsed laser, such as a gallium arsenide (GaAs) laser, with a peak power capability of approximately one watt and an average power of 100 mW (milliwatts) or more. Fundamental device limits, such as multimode effects and optical damage at higher power levels, preclude the achievement of these powers from a single laser device.
Various attempts have been made to combine multiple laser outputs into a single source, but with only limited success. One approach has been to place multiple lasers in a linear array, and to rely on coupling between them to achieve some degree of phase locking. Unfortunately, coupling between the adjacent lasers is not sufficient to produce a coherent beam and a desirable far-field pattern of radiation distribution. Moreover, the use of a linear array yields a similarly proportioned linear far-field pattern, which in most cases is less desirable than a more nearly circular pattern.
Use of an optical star coupler has been suggested as a better approach to combining the outputs of multiple lasers, but this has required precise phase alignment of the lasers. Although phase alignment can be achieved with the help of trimming adjustments while the lasers are active, there is no assurance that the alignment will be maintained under conditions of varying temperature and other parameters.
Accordingly, there is still a need for a technique for combining the outputs of multiple lasers in such a manner that a single coherent source is obtained, with a concentrated far-field distribution pattern. The present invention satisfies this need.